GM Service Manual Online
For 1990-2009 cars only

The design of the passlock™ system is to prevent the vehicle operation if the proper ignition key is not used in order to start the vehicle. The mechanical key, in normal operation, will turn the passlock™ lock cylinder. The passlock™ sensor will relay the passlock™ data to the passlock™/EVO module. The passlock™/EVO module will determine the validity of the passlock™ data. The passlock™ module will send a code password to the vehicle control module (VCM). When the VCM receives the correct code the VCM allows the fuel injectors to operate normally. The passlock™ system requires the vehicle control module (VCM) and the passlock™/EVO module to communicate the various functions in order to operate. These functions transmit over the class 2 serial data line CKT 1807. For an explanation of the class 2 serial data operation refer to Data Link Connector Circuit Description in Wiring Systems